Along with the deployment of more and more local nodes such as Femtocells, micro cells and relays, conventional network architecture mainly based on macro base stations is gradually evolving into network architecture in which various kinds of base stations exist, so as to provide multilayered network coverage. In order to improve performances of the network architecture including various kinds of base stations, a network architecture, in which coordination/aggregation among multiple evolved Node-Bs (eNBs) is achieved via non-ideal link, has been proposed. In this architecture, some Radio Bearers (RBs) for a User Equipment (UE) are in a Master Cell Group (MCG) managed by a Master eNB (MeNB), and these RBs include control-plane bearers, i.e., Signaling Radio Bearers (SRBs), and user-plane bearers, i.e., Data Radio Bearers (DRBs). A Primary Cell (PCell) is provided with a Physical Uplink Control Channel (PUCCH). In addition, some other RBs for the same UE are in a Secondary Cell Group (SCG) managed by a Secondary eNB (SeNB), and a special cell is provided with a PUCCH. The UE communicates with two eNBs in this architecture, and this situation is called as Dual Connectivity (DC). In the case that the UE needs to perform inter-frequency measurement, a measurement gap needs to be configured by a network for the UE. In the case that the measurement gap is configured for some cells while the other cells operate normally, data transmissions in the other cells may be interrupted when the UE performs the inter-frequency measurement.
Relevant technologies are described hereinafter.
1. DC Technology
In a possible multilayered network coverage environment as shown in FIG. 1, a non-ideal data/signaling interface, i.e., an Xn interface, is adopted between the MeNB and the SeNB, and the UE may communicate with the MeNB and the SeNB simultaneously. In the case that the UE communicating with the MeNB enters the coverage of a cell managed by the SeNB, the MeNB may transfer a part of or all of the data/signaling of the UE to the SeNB based on signal intensity or load balancing, so that the UE is served by the SeNB. At this time, the UE may use resources from the MeNB and the SeNB simultaneously, so as to achieve the inter-eNB aggregation. In this scenario, multiple RBs of the UE may be in the SCG and the MCG, and the RBs associated with the SeNB may include DRB and/or SRB.
2. DC Architecture
FIG. 2 shows a first kind of the DC architecture, where the UE has independent bearers for both the MeNB and the SeNB. Each eNB includes an independent Packet Data Convergence Protocol (DPCP) entity for the UE.
FIG. 3 shows a second kind of the DC architecture, where a connection between the UE and the MeNB has an independent bearer. For achieving a connection between the UE and the SeNB, a part of data carried on one Evolved Packet System (EPS) bearer of the MeNB is allocated to, and transmitted on, the SeNB. The DPCP entity of the EPS bearer is still in the MeNB, and an independent Radio Link Control (RLC) entity is in the SeNB.
3. Measurement Gap
During the inter-frequency measurement, the UE may not receive and transmit the data at a current serving frequency normally, so a measurement gap needs to be configured by a network side for the UE, so as to perform the inter-frequency measurement without any packet loss. The configuration of the measurement gap needs to meet the following requirements. The measurement gap may be configured in accordance with different gap patterns. For example, for gap pattern 0, the measurement gap is 6 ms, and a measurement gap repetition period is 40 ms.
TABLE 1Measurement gap configuration supported by UEMinimum availabletime forMeasurementinter-frequency andGapinter-RATGapMeasurementRepetitionmeasurementsPatternGap LengthPeriodduring 480 ms periodMeasurementID(MGL, ms)(MGRP, ms)(Tinter1, ms)Purpose064060Inter-FrequencyE-UTRAN FDDand TDD,UTRAN FDD,GERAN, LCRTDD, HRPD,CDMA2000 1x168030Inter-FrequencyE-UTRAN FDDand TDD,UTRAN FDD,GERAN, LCRTDD, HRPD,CDMA2000 1x
4. Adjustment of Receiver of UE
In the case that multiple serving frequencies are configured by the network for the UE, the network may issue an activation command, so as to activate the serving frequency for the UE. After the receipt of the activation command, the UE may adjust its receiver. In the case that an identical receiver is shared, an interruption period caused by the adjustment of the receiver is 5 ms, and in the case that the UE has multiple independent receivers, the interruption period caused by the adjustment is 1 ms. Because the network is aware of a time point where the UE adjusts its receiver, no data transmission is scheduled during the adjustment, so as to prevent the packet loss due to the adjustment. However, the network does not known a type of the receiver of the UE, so based on the interruption period of 5 ms, the data transmission may not be scheduled within a time period specified in a protocol.
5. Measurement Gap Configuration for DC
Measurement gap configuration set for UE: the measurement gap configuration issued by the network to the UE is applied to all the serving frequencies, and within the measurement gap, the UE should not perform the reception and transmission of the data at all the serving frequencies.
Measurement gap configuration set for eNB (or cell group): the measurement gap configuration issued by the network to the UE is applied to a part of the serving frequencies, e.g., SCG or MCG, and within the measurement gap, the UE only should not perform reception and transmission of the data at these serving frequencies configured with the measurement gap.
In a word, in the case of DC, there is no solution for interruption caused by the measurement gap. In the case that a measurement gap is configured by the MeNB for the MCG associated with the UE or another measurement gap is configured by the SeNB for the SCG associated with the UE, the UE may adjust the frequency for the receiver at the beginning and end of the measurement. At this time, in the case that the SeNB (or MeNB) cannot know the measurement gap configured for the MCG (or SCG), packet loss may occur at the SeNB during the adjustment of the receiver of the UE. In addition, in the case that a measurement gap is configured by the MeNB for the UE but the SeNB does not know this measurement gap configuration, the packet loss may also occur.